In general, renewable energy power gains very small share of global electricity market. However, due to the limited fossil fuels resource and their negative impacts on the environment, the industry is being urged to improve and upgrade renewable energy technology. Other than using renewable energy to replace fossil fuels, environmental energy can be further collected for the reuse. Among these research areas, a thermoelectric material (TEM) and an energy harvesting (EH) are two hot research topics.
Many energy sources have the maximum power point (MPP) characteristic, for example, FIG. 1 shows a characteristic curve of the output current versus (vs.) the output voltage of a thermoelectric (TE) energy source (for example, TE Generator. TEG) and a characteristic curve of the output power vs. the output voltage of a TE energy source (for example, TEG). In the upper part (a) of FIG. 1, the abscissa represents output voltage VTE of the TE energy source and the ordinate represents output current ITE of the TE energy source; in the lower part (b) of FIG. 1, the abscissa represents output voltage VTE of the TE energy source and the ordinate represents output power PTE of the TE energy source. It can be seen from FIG. 1 that the larger the output current ITE of the TE energy source is, the smaller the output voltage VTE thereof is. When the output voltage VTE of the TE energy source is set at an operation voltage VOP shown by FIG. 1, the output power PTE achieves the maximum power value PMAX (that is, the MPP).
Another example is given by FIG. 2, wherein a characteristic curve of the output current vs. the output voltage of a photovoltaic cell (PV cell) and a characteristic curve of the output power vs. the output voltage of a PV cell are illustrated. In the upper part (a) of FIG. 2, the abscissa represents output voltage VPV of the PV cell and the ordinate represents output current IPV of the PV cell; in the lower part (b) of FIG. 2, the abscissa represents output voltage VPV of the PV cell and the ordinate represents output power PPV of the PV cell. It can be seen from FIG. 2 that the larger the output current IPV of the PV cell is, the smaller the output voltage VPV thereof is. When the output voltage VPV of the PV cell is set at an operation voltage VOP shown by FIG. 2, the output power PPV achieves the maximum power value PMAX (that is, the MPP).
During employing and operating an energy source with the MPP characteristic, it is needed to track the power point on the output of the energy source to advance the power-generating efficiency.